This invention relates to a detector apparatus, and more particularly, to an apparatus for detecting the difference in frequency between the frequency of two electrical signals being supplied by two different frequency sources.
In previous frequency deviation circuits, a single D-type flip flop is used to generate a signal indicative of the difference between the frequencies of two signals, a first signal being applied to a D input of the D-type flip flop, and a second signal being applied to the clock input of the D-type flip flop. The frequency of the first signal is F.sub.1 and the frequency of the second signal is F.sub.2, the output of the single type flip flop being F.sub.1 -F.sub.2. This relatively simple circuit is, however, very susceptible to jitter between the two frequencies F.sub.1 and F.sub.2 and can exhibit metastable conditions when the two single are in phase.
The detection circuit of the present invention outputs a signal indicative of the difference between the two signals (F.sub.1 -F.sub.2), and is an improvement over the single D-type flip flop in that it is not susceptible to jitter between the edges of the two input signals F.sub.1 and F.sub.2. Further, potential metastable conditions are eliminated.
Thus there is provided by the present invention a detector circuit for detecting the differences of frequency between two signals and is not susceptible to jitter between the two signals. The two signals of the preferred embodiment are digital signals.